A mongrel dog named Rocco helped make history in a Tuscan wood when he led his owners to a 1.5kg (3.3lb) white truffle, the largest unearthed in half a century and now expected to break auction records.

"I had to tie Rocco up, he was so excited," said truffle hunter and trader Cristiano Savini, who spent more than an hour on his hands and his knees with his father, Luciano, carefully digging down 80cm (2.6ft) to find the truffle at a secret countryside spot near Pisa on Friday.

As crowds gathered at a local truffle fair over the weekend to breathe in what Savini described as "the incredible smell" of the truffle - second in size to a 2.5kg truffle found in 1954 and presented to President Eisenhower - news spread, and the knobbly, soil encrusted truffle will now go under the hammer on Saturday in Macau during a charity auction attended by millionaires flying in from Hong Kong.

"We hope to get the truffle blessed by the Pope before it flies out, but things need to move fast as white truffles should be eaten within 20 days," said auction organiser Giselle Oberti. "I expect we can beat the record €140,000 paid for a smaller white truffle recently."

Rarer and more pungent than black truffles, the white tuber magnatum pico is found in Italy and Croatia, although yields are down this year after a dry summer. "The truffle we found benefited from the 15 days of rain we have just had," said Savini.

The weekend auction will be held at three sites linked by satellite in Macau, Florence and at the Refettorio restaurant in London run by Italian chef Giorgio Locatelli. Locatelli said the successful bidder should eat the truffle fast to avoid the fate of the 700g specimen for which a group said to include Roman Abramovich and Gwyneth Paltrow bid £28,000 at another charity auction in 2004, only to see it go mouldy in the safe of a London restaurant. "Keep truffles simple," he advised. "Risotto with white truffle is the king since the rice keeps its heat and makes the truffle sweat and release flavour."

Despite the thousands of pounds set to be paid for his find, Savini said he was happy to see it all go to charity. "This truffle was a gift from God," he explained. Rocco the dog would, however, be rewarded with a new kennel.